Diethylene glycol (DEG) + H2O solutions (DEGWs) were used as the promising medium for the absorption processes of SO2. In this work, when UV, FTIR, H-1 NMR, and fluorescence spectroscopic techniques were used for inspection of spectral changes of DEGWs with increasing SO2 concentration, the results suggest that H2O can interact with DEG by hydrogen bonds as the formation of -CH2CH2O(H)(center dot center dot center dot)-HOH center dot center dot center dot- and -CH2-CH2-O(CH2-CH2-)(center dot center dot center dot)-HOH center dot center dot center dot- in DEGWs. Furthermore, SO2 can interact with DEG in various DEGWs by hydrogen bonds as the formation of -CH2CH2OH center dot center dot center dot-OSO center dot center dot center dot- and the intermolecular S-center dot center dot center dot-O interaction in the absorption processes of SO2, which was not discussed in the previous similar systems. The results of this work can be used to provide an important absorption mechanism for the design and operation of the absorption and desorption process in flue gas desulfurization with potential industrial application of DEG aqueous solutions.